It is widely proclaimed that April Fool’s Day originated in France in 1562, or thereabouts, when Pope Gregory replaced the Julian calender with the Gregorian calender in the Julian calender month of April. The day of introduction of the Gregorian calender was made the first day of January. Some people hadn’t heard about the change in the date, so they continued to celebrate the New Year’s Day, but it being 1st April. So, others called them “April fools.”
The fact is that Pope Gregory XIII ordered Thursday 4 October 1582 to be the last day of the Julian calendar. The next day was Friday 15 October. April Fool’s Day is an April Fool’s tale.
The April Fool’s Day tradition in France includes poisson d’avril (“April’s fish”), attempting to attach a paper fish to the victim’s back without being noticed.
“April 1st: This is the day upon which we are reminded of what we are on the other three-hundred and sixty-four.” – Mark Twain